If you followed my Fishing guide then you are pretty well prepared for this one. Armed with the fish that you fished up going after 99/120 you will now be able to get 99/120 cooking.
Do note. That you will need extra fish than what you caught getting to 99/120 fishing. Do to burn rates and the exp rate differences.
This Guide is fairly Simple and straight foward.
At home Ascend the beam to the second floor (First floor for those in certian countrys)
On the second floor go into the WESTERN room.
Here is a bank chest and a range very close to each other.
Now that you are here Cook everything that you fished up going for 99/120 fishing. And cook them until you run out of that one and move onto the next. Levels 1 - 40 - Shrimp
Levels 15 - 40 - Anchovies
Levels 40 - 62 - Lobsters
Levels 62 - 80 - Monkfish
Levels 80 - 88 OR 80 - 99 - Sharks
Levels 88 - 93 - Cavefish
Levels 93 - 99/120 - Rocktails
Also go to Varrock East Bank and just south east of that go talk to Dimintheis. He will give you cooking gaunts.